1. Field of the Invention
This invention relates to an image forming apparatus for use in a copying machine, a printer, a plotter, a facsimile machine or similar machine.
2. Description of Related Art
One type of conventional image forming apparatus uses an electrode having plural opening portions (hereinafter referred to as "apertures") as disclosed in U.S. Pat. No. 3,689,935. In this image forming apparatus, a voltage is applied to the electrode while being modulated according to image data to thereby control the passage of toner through the apertures and form an image on a supporter with the passed toner.
This image forming apparatus includes an insulating flat plate, a continuous reference electrode formed on one surface of the flat plate, and plural control electrodes formed on the other surface of the flat plate and electrically insulated from one another. The apparatus further includes an aperture electrode member having at least one array of apertures, each of which is provided in correspondence with each control electrode to penetrate through the flat plate, the reference electrode and the control electrode. Also provided are means for selectively applying potential between the reference electrode and each of the control electrodes and means for supplying charged toner to modulate the flow of toner that has just passed through the apertures according to the supplied potential. There is also means for positioning the supporter in a toner-particle flowing passage such that the supporter and the aperture electrode member are movable relative to each other. In the image forming apparatus thus constructed, a back electrode roller is rotatably disposed to confront the aperture electrode yet be spaced from the aperture electrode, for example, by 1 mm (that is, to maintain a 1 mm gap therebetween.)
However, in the conventional image forming apparatus described above, the toner is likely to adhere to the apertures of the aperture electrode member so that the apertures become clogged with toner. This clogging of the toner disturbs the formation of an image. In addition, toner that has already adhered to the supporter can then fall down from the supporter and become laminated on the aperture electrodes. The laminated toner from the aperture electrodes will then adhere to a fed supporter and disturb an image on the supporter.
To solve the above problems, the aperture electrode member must be periodically cleaned. However, as described above, the gap between the aperture electrode member and the back electrode roller is kept to about 1 mm. Thus, the cleaning work is very difficult..